The present invention relates to a process of transfer printing to apply a beautiful print onto uneven objects having grooves, projections, curved surface, etc.
There is known from U.S. Pat. No. 4,010,057 a printing apparatus wherein a thin film on which a pattern is printed is floated on the surface of a liquid and the pattern is transferred onto the surface of an object to be printed with the pattern utilizing the liquid pressure by submerging the object into the liquid while pressing the object onto the thin film (cf. Abstract of the Patent). The patent describes that it is the most preferable to use the farinaceous film as thin film, and in addition, the materials of the thin film can be polyacrylic acid soda, polyvinyl alcohol, methyl cellulose, carboxymethylcellulose, polyethylene oxide, polyvinylpyrrolidone and acrylic acid amide as synthetic high molecular substances; glue, gelatin, casein and polypeptide from among high molecular substances; starch, cellulose, dextrin, alubmin, soy bean protein, gum arabic and tragacanth gum from among vegetable high molecular substances; and sea weed glue, Japanese gelatin and alginic acid soda among sea weed high molecular substances.
However, the thin film made of the above-mentioned materials does not show a strength and elongation sufficient for multi-color printing, a good swellability, namely a good extensibility on the surface of the water as explained after and a large flexibility and softening property, so that the thin film is hard to closely adhere to an uneven surface of an object to be printed. Among a large number of materials listed above, the only practically usable material is a polyvinyl alcohol resin.
The thin film of a polyvinyl alcohol resin also has the following defects. That is, since the thin film largely extends and often partially dissolves in water to be torn and scatters when floated on the surface of the water, a pattern printed on the thin film is hard to be accurately transferred to the object. Also, since the period suitable for pressing an object to be printed onto the thin film is short, mistransfer is easy to occur. Further, in case of printing an object having a complicated curved surface, an acute part or a concave part, a spherical object or a longitudinally lengthy object, cutting, disturbance or overlapping of a printed pattern may occur.